ZOOLOGY AND HUMAN NVELFARE 



human diseases there is none which is of more importance 

 in the world to-day than malaria ... It has been esti- 

 mated to be the direct or indirect cause of over one-half 

 the entire mortality of the human race. Sir Ronald Ross 

 says that in India alone it is officially estimated that 

 malaria kills over one million persons a year." The fright- 

 ful effects of syphilis are commonly known in some degree, 

 though not fully realized by most people; and hookworm 

 disease has social consequences of tremendous importance. 



Parasitism, the living of one organism on or in another, 

 at the latter' s expense, is a widespread phenomenon, of 

 which these disease-producing parasites are especially 

 striking examples. They happen to have great medical 

 and popular interest, but the researches carried out in 

 discovering and identifying them, in learning their life 

 histories, and in getting a biological basis for successful 

 treatment, are essentially zoological in character. To 

 illustrate this point, we may look briefly at two of the 

 diseases mentioned above. 



Malaria is a common disease throughout the warmer 

 portions of the world and has been recognized from early 

 times as being especially prevalent near swamps and ponds. 

 In its several varieties it causes feverish conditions in its 

 victims and leads to anemia, general weakness, suscepti- 

 bility to other diseases, and frequently to coma and death 

 from obstruction of the circulation in the brain. Sometimes 

 infected individuals recover and become immune; but, in 

 general, the result of the disease, when it is common in a 

 population, is to lower the average vitality and thus to 

 produce sociological degeneration. There is a strong 

 probability that certain ancient civilizations, especially 

 the Grecian, fell into decline because of this disease; and 

 the backward condition of many affected districts, even 

 at the present time, seems certainly to have the same 

 explanation. 



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